Conductive ink composition and conductive film

Abstract

An electroconductive ink composition comprising a (meth)acrylic polymer (A) and silver particles (B), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight-average molecular weight of 500,000 or higher, and a hydroxyl value exceeding 50 mgKOH / g and the silver particles (B) have a specific surface area of 0.5-3.0 m2 / g, a 50% average particle diameter of 0.5-14.0 μm, and a maximum particle diameter of 8 μm or larger, the electroconductive ink composition having a solid content of 50-80 mass%; and an electroconductive ink composition comprising a (meth)acrylic polymer (A) and carbon black (CB), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight-average molecular weight of 500,000 or higher, and a hydroxyl value exceeding 50 mgKOH / g and the carbon black (CB) has a specific surface area of 50 m2 / g or larger and an aggregate diameter of 400 nm or less, the electroconductive ink composition having a solid content of 15-30 mass%.

Description

[Technical Field]

[0001] The present invention relates to a conductive ink composition and a conductive film using the conductive ink composition. This application claims priority based on Patent Application Nos. 2021-191276 and 2021-191277, filed in Japan on November 25, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, printed electronics (PE), which uses conductive ink to form conductive films by printing, has been attracting attention in the field of electronic device manufacturing. By using PE, for example, it is possible to form conductive films on thin substrates and manufacture flexible devices.

[0003] Patent Document 1 aims to make electrodes and wiring in flexible wiring boards stretchable and to reduce changes in electrical resistance due to stretching, and proposes a method in which metal filler particles of a specific shape are filled into an elastomer that has functional groups capable of hydrogen bonding and has a glass transition temperature of -10°C or lower, and the flake-shaped or needle-shaped metal filler particles are oriented in the stretching direction of the film and brought into contact with the chunk-shaped metal filler particles to ensure conductivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-153364 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the findings of the present inventors, the method described in Patent Document 1 may not be able to achieve sufficient elongation. An object of the present invention is to provide a conductive ink composition that can form a conductive film that is stretchable and has excellent conductivity when stretched. [Means for solving the problem]

[0006] The present invention has the following aspects. [1-1] A composition comprising a (meth)acrylic polymer (A) and silver particles (B), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight-average molecular weight of 500,000 or higher, and a hydroxyl value of more than 50 mgKOH / g, and the silver particles (B) have a specific surface area of ​​0.5 to 3.0 m 2 / g, a 50% average particle size of 0.5 to 14.0 μm, a maximum particle size of 8 μm or more, and a solid content of 50 to 80 mass %. [1-2] The conductive ink composition according to [1-1], wherein the (meth)acrylic polymer (A) has a glass transition temperature of more than -50°C and less than -30°C and a weight average molecular weight of 500,000 to 990,000. [1-3] The conductive ink composition according to [1-1] or [1-2], wherein the content of units (a1) derived from a hydroxyl group-containing monomer relative to all units constituting the (meth)acrylic polymer (A) is 20 to 40 mass %. [1-4] The conductive ink composition according to any one of [1-1] to [1-3], which has a viscosity at 23°C of 20 to 50 Pa·s. [1-5] A conductive film obtained by drying a coating of the conductive ink composition according to any one of [1-1] to [1-4] above. [1-6] The conductive film of [1-5] used for electrodes or wiring that require stretchability in electronic devices. [1-7] The conductive film of [1-5] used for the detection part, electrode, or wiring of a resistance change sensor. [2-1] A composition comprising a (meth)acrylic polymer (A) and carbon black (CB), wherein the (meth)acrylic polymer (A) has a glass transition temperature of 0°C or lower, a weight average molecular weight of 500,000 or higher, and a hydroxyl value of more than 50 mgKOH / g, and the carbon black (CB) has a specific surface area of ​​50 m 2 / g or more, an aggregate diameter of 400 nm or less, and a solid content of 15 to 30 mass %. [2-2] The conductive ink composition according to [2-1], wherein the (meth)acrylic polymer (A) has a glass transition temperature of more than -50°C and less than -30°C and a weight average molecular weight of 500,000 to 990,000. [2-3] The conductive ink composition according to [2-1] or [2-2], wherein the content of units (a1) derived from a hydroxyl group-containing monomer relative to all units constituting the (meth)acrylic polymer (A) is 20 to 40 mass %. [2-4] The conductive ink composition according to any one of [2-1] to [2-3], which has a viscosity at 23°C of 20 to 100 Pa·s. [2-5] A conductive film obtained by drying a coating of the conductive ink composition according to any one of [2-1] to [2-4] above. [2-6] The conductive film of [2-5] used for electrodes or wiring that require stretchability in electronic devices. [2-7] The conductive film of [2-5] used in the detection part, electrode, or wiring of a resistance change sensor. [Effects of the Invention]

[0007] The conductive ink composition of the present invention can form a conductive film that is stretchable and has excellent conductivity when stretched.

[0008] The following definitions of terms apply throughout the specification and claims. A numerical range expressed by "to" means that the numerical values ​​before and after "to" are the lower and upper limits of the numerical range. "(Meth)acrylate" is a general term for acrylate and methacrylate, and "(meth)acrylic" is a general term for "acrylic" and "methacrylic." The term "unit" of a polymer refers to an atomic group (monomer unit) formed from one monomer molecule.

[0009] The weight-average molecular weight (Mw) of a polymer is a polystyrene-equivalent molecular weight obtained by gel permeation chromatography using a calibration curve prepared using standard polystyrene samples of known molecular weight. More specifically, the weight-average molecular weight (Mw) can be determined using, for example, a GPC measurement device manufactured by Nihon Waters Co., Ltd., product name "Alliance E2695 Separation Module," under the following GPC measurement conditions, using a polystyrene-equivalent value. (GPC measurement conditions) Sample concentration: 0.5 wt% (tetrahydrofuran solution) Sample injection volume: 20 μL Eluent: tetrahydrofuran (THF) ·Flow rate (flow rate): 0.3mL / min Column temperature (measurement temperature): 40℃ Column: Product name: "TSKguard column HSPgel RT-MB-H+ HSPgel RT-2.0" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI), product name "Alliance2414" (manufactured by Nihon Waters Co., Ltd.)

[0010] The hydroxyl value (unit: mgKOH / g) of a polymer is a theoretically calculated value. It is calculated from the following formula (1). In the following formula (1), the "copolymerization amount of monomers having hydroxyl groups" means the ratio (unit: mass %) of monomers having hydroxyl groups to all monomers constituting the polymer.

[0011]

number

[0012] The glass transition temperature of the copolymer obtained by polymerizing the monomer mixture is Tg (theoretical value) calculated by the Fox equation (2) using the known glass transition temperatures of the homopolymers of each monomer. The glass transition temperature of the homopolymer of the monomer can be, for example, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003). In the following formula (2), Tg is the glass transition temperature of the copolymer (unit: K), Tg1 is the glass transition temperature of the homopolymer of monomer 1 (unit: K), Tg2 is the glass transition temperature of the monomer 2 homopolymer (unit: K), Tg n is the glass transition temperature of the homopolymer of monomer n (unit: K), W1 is the weight fraction of monomer 1 in the monomer mixture, W2 is the weight fraction of monomer 2 in the monomer mixture, W n represents the weight fraction of monomer n in the monomer mixture.

[0013]

number

[0014] The viscosity of the conductive ink composition is a value measured using a rheometer. It is the viscosity measured at a shear rate of 5.1 (unit: 1 / s). The viscosity measurement temperature was 23°C unless otherwise specified.

[0015] First Embodiment <Conductive ink composition> The conductive ink composition of the first embodiment (hereinafter also referred to as the "first composition") contains a (meth)acrylic polymer (A) and silver particles (B). In this specification, the specific surface area of ​​silver particles is a value measured by the BET method, in which a mixed gas of helium and nitrogen is adsorbed onto silver particles and the specific surface area of ​​the silver particles is measured from the amount of the adsorbed mixed gas. In this specification, the maximum particle size and 50% average particle size of silver particles refer to the maximum particle size and the median size at 50% cumulative volume in a particle size distribution curve measured by laser diffraction particle size measurement.

[0016] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) is a polymer containing units based on (meth)acrylate. The content of units based on (meth)acrylate relative to all units constituting the (meth)acrylic polymer (A) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass.

[0017] The (meth)acrylic polymer (A) preferably contains one or more units (a1) derived from a hydroxyl group-containing monomer. The units (a1) contribute to the hydroxyl value of the (meth)acrylic polymer (A). The unit (a1) is preferably a unit based on a (meth)acrylate having a hydroxyl group. Specific examples of the hydroxyl group-containing monomer (a1) corresponding to the unit (a1) include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and 2-hydroxyethyl methacrylate. The content of units (a1) relative to all units in the (meth)acrylic polymer (A) is preferably 20 to 40% by mass, more preferably 22 to 38% by mass, and even more preferably 24 to 36% by mass. When the content of units (a1) is at least the lower limit of the above range, a hydroxyl value of more than 50 mgKOH / g is likely to be obtained, and affinity with silver particles is increased, resulting in excellent elasticity. When the content is at most the upper limit, the self-cohesion force of the meth(acrylic) polymer is not too strong, and good dispersibility and good elasticity during ink production are likely to be obtained.

[0018] The (meth)acrylic polymer (A) preferably contains one or more units (a2) based on a (meth)acrylate having an alkyl group having a carbon number of 4 to 12. The units (a2) do not contain units (a1). The alkyl group having 4 to 12 carbon atoms in the unit (a2) may be linear or branched. Specific examples of the (meth)acrylate (a2) corresponding to the unit (a2) include n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The content of units (a2) relative to all units of the (meth)acrylic polymer (A) is preferably 46 to 64 mass%, more preferably 48 to 62 mass%, and even more preferably 50 to 60 mass%. When the content of units (a2) is at least the lower limit of the above range, good durability during stretching is likely to be obtained. When it is at most the upper limit, the polymer is less likely to become rigid and good stretchability is likely to be obtained.

[0019] The (meth)acrylic polymer (A) preferably contains one or more units (a3) ​​based on a (meth)acrylate having an alkyl group having 1 to 3 carbon atoms. The units (a3) ​​do not contain the units (a1) and the units (a2). The alkyl group having 3 carbon atoms in the unit (a3) ​​may be linear or branched. Specific examples of the (meth)acrylate (a3) ​​corresponding to the unit (a3) ​​include methyl (meth)acrylate and ethyl (meth)acrylate. The content of units (a3) ​​relative to all units of the (meth)acrylic polymer (A) is preferably 6 to 19 mass%, more preferably 8 to 17 mass%, and even more preferably 10 to 15 mass%. When the content of units (a3) ​​is at least the lower limit of the above range, excellent flexibility and sufficient stretchability are likely to be obtained. When the content is at most the upper limit, excellent adhesion to the substrate and good durability during stretching are likely to be obtained.

[0020] The (meth)acrylic polymer (A) preferably contains one or more units (a4) derived from a carboxyl group-containing monomer, and the units (a4) do not include the units (a1), (a2), and (a3). Specific examples of the carboxy group-containing monomer (a4) corresponding to the unit (a4) include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and acid anhydride group-containing monomers (maleic anhydride, itaconic anhydride, etc.). The content of units (a4) relative to all units of the (meth)acrylic polymer (A) is preferably 0.05 to 0.35 mass%, more preferably 0.10 to 0.30 mass%, and even more preferably 0.15 to 0.25 mass%. When the content of units (a4) is at least the lower limit of the above range, excellent affinity with silver particles is obtained, and sufficient stretchability is easily obtained. When the content is at most the upper limit, the cohesive force of (meth)acrylic acid is not too high, and good stretchability is easily obtained.

[0021] The (meth)acrylic polymer (A) may contain one or more units (a5) derived from other monomers copolymerizable with the units (a1) to (a4) other than the above units (a1) to (a4). Examples of other monomers (a5) corresponding to the unit (a5) include (meth)acrylates having a linear or branched alkyl group having 13 to 20 carbon atoms, (meth)acrylates having an aromatic ring, (meth)acrylates having a non-aromatic cyclic hydrocarbon group, epoxy group-containing (meth)acrylates, vinyl ester-based monomers, styrene-based monomers, olefin-based monomers, vinyl ether-based monomers, and polyfunctional monomers. For example, vinyl ester monomers such as vinyl acetate and vinyl propionate are preferred. The content of units (a5) relative to all units in the (meth)acrylic polymer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less, and may be zero.

[0022] The glass transition temperature of the (meth)acrylic polymer (A) is 0°C or lower, preferably lower than -30°C, and more preferably lower than -32°C. When the glass transition temperature is equal to or lower than the upper limit, drying properties during the production of a conductive film can be ensured, and a good elongation rate can be obtained. The lower limit of the glass transition temperature is preferably higher than -50°C, and more preferably higher than -45°C. When the glass transition temperature of the (meth)acrylic polymer (A) is higher than -50°C, the conductive film has excellent durability and is likely to have sufficient stretchability.

[0023] The weight-average molecular weight of the (meth)acrylic polymer (A) is 500,000 or more, preferably 520,000 or more, and more preferably 540,000 or more. When the weight-average molecular weight is equal to or greater than the lower limit, the durability of stretchability is excellent. The upper limit of the weight-average molecular weight is preferably 990,000 or less, more preferably 950,000 or less, and even more preferably 900,000 or less, from the viewpoint of ensuring flexibility and exhibiting conductivity.

[0024] The hydroxyl value of the (meth)acrylic polymer (A) is greater than 50 mgKOH / g, preferably 75 mgKOH / g or greater, and more preferably 100 mgKOH / g or greater. When the hydroxyl value exceeds 50 mgKOH / g, the affinity between the silver particles and the (meth)acrylic polymer is moderately high, resulting in excellent elasticity. The upper limit of the hydroxyl value is preferably 200 mgKOH / g or less, more preferably 175 mgKOH / g or less, and even more preferably 150 mgKOH / g or less, from the viewpoint of not impairing the conductivity of the silver particles.

[0025] The (meth)acrylic polymer (A) may be produced by a conventional method, or a commercially available product may be used. The (meth)acrylic polymer (A) may be used in the form of a (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and an optional solvent. The solid content of the (meth)acrylic polymer composition is not particularly limited, but from the viewpoint of handling during blending, a viscosity that imparts appropriate fluidity is desirable. For example, a solid content of 10% to 50% by mass is preferred, and 20% to 40% by mass is more preferred.

[0026] A preferred embodiment of the (meth)acrylic polymer (A) is, for example, the following embodiment (i). [Aspect (i)] The content of the unit (a1) is 20 to 40 mass %; The content of units (a2) is 46 to 64% by mass, The content of units (a3) ​​is 6 to 19% by mass, The content of the unit (a4) is 0.05 to 0.35 mass %, The content of units (a5) is 10% by mass or less, The glass transition temperature is greater than -50°C and less than -30°C, The weight average molecular weight is 500,000 to 990,000, A (meth)acrylic polymer having a hydroxyl value of more than 50 mgKOH / g and not more than 200 mgKOH / g. The total of the units (a1) to (a5) does not exceed 100% by mass.

[0027] <Silver particles (B)> Silver particles (B) have a specific surface area of ​​0.5 to 3.0 m 2 / g, a 50% average particle size of 0.5 to 14.0 μm, and a maximum particle size of 8 μm or more. The silver particles (B) preferably have a shape that is flat in one direction, such as a flake or scale shape. The specific surface area is 0.7 to 3.0 m 2 The 50% average particle size is more preferably 1.0 to 12.0 μm. The surfaces of the silver particles (B) may be coated with an organic acid. Specific examples of the organic acid include stearic acid, oleic acid, lauric acid, and hexanoic acid. However, the organic acid is not limited to these specific examples. The use of silver particles (B) that satisfy the above conditions makes it easier to obtain a conductive film that exhibits excellent conductivity when stretched. Furthermore, the combination of a (meth)acrylic polymer (A) and silver particles (B) that satisfy the above conditions makes it possible to obtain a conductive film that is less likely to crack or break when stretched and that exhibits conductivity even when highly stretched.

[0028] <Solvent (C)> The first composition may optionally contain one or more solvents (C). The solvent (C) is not particularly limited as long as it can uniformly disperse the (meth)acrylic polymer (A) and the silver particles (B), has low volatility, keeps the ink viscosity stable, and can be removed in the drying step during the formation of the conductive film. Examples of the solvent (C) include ester-based solvents such as diethylene glycol monoethyl ether acetate (also known as ethyl carbitol acetate), hydrocarbon-based solvents such as decane, tetradecane, and cyclohexane, and alcohol-based solvents such as 2-ethylhexanol, 2-ethylhexyl ether derivatives, and diethylene glycol monobutyl ether.

[0029] <Optional ingredients> The first composition may contain optional components other than the (meth)acrylic polymer (A), silver particles (B), and solvent (C) to the extent that the effects of the present invention are not impaired. As the optional components, components known in the field of conductive ink compositions can be used. For example, in order to improve printability, components that adjust the interfacial tension of the ink (e.g., surfactants, leveling agents, etc.), components that adjust the viscosity of the ink (e.g., thixotropic agents), etc. may be blended. In addition, in order to improve adhesion to each substrate, it is possible to blend a binder component other than the (meth)acrylic polymer (A). Examples of binder components include polyurethane polymers, epoxy polymers, ester polymers, terpene resins, and terpene resin derivatives (e.g., terpene phenol resins). The binder component can be blended in an amount that does not impair elasticity. In addition, an ion scavenger can be added to prevent migration.

[0030] The solid content is 50 to 80% by mass, preferably 52 to 78% by mass, and more preferably 54 to 76% by mass, based on the total mass of the first composition. When the solid content is within the above range, sufficient extensibility and good conductivity when stretched are easily obtained. Furthermore, viscosity suitable for printing is easily obtained. The solid content can be adjusted by the content of the solvent (C).

[0031] The viscosity of the first composition is preferably 20 to 50 Pa·s, more preferably 24 to 46 Pa·s, and even more preferably 28 to 42 Pa·s. When the viscosity is within the above range, good printability is likely to be obtained. For example, properties suitable for screen printing are likely to be obtained. For example, if the viscosity of the first composition is too high, clogging or rubbing may occur during printing, whereas if the viscosity is too low, printing defects such as bleeding and dripping may occur.

[0032] The content of the (meth)acrylic polymer (A) relative to the solid content of the first composition is preferably 3.0 to 10.5% by mass, more preferably 4.0 to 10.0% by mass, and even more preferably 4.5 to 9.5% by mass. When the content of the (meth)acrylic polymer (A) is equal to or greater than the above-mentioned lower limit, sufficient stretchability is easily obtained. When the content is equal to or less than the above-mentioned upper limit, a sufficient content of silver particles (B) is easily ensured, and good conductivity during stretching is easily obtained. The content of silver particles (B) relative to the solid content of the first composition is preferably 80.0 to 97.0 mass%, more preferably 85.0 to 96.5 mass%, and even more preferably 90.0 to 96.0 mass%. When the content of silver particles (B) is at least the above lower limit, good electrical conductivity is likely to be obtained, while when it is at most the above upper limit, a sufficient content of components other than silver particles (B) is likely to be secured, and good properties such as stretchability are likely to be obtained. The content of the optional components relative to the solid content of the first composition is preferably 10% by mass or less, more preferably 5% by mass or less, and may be zero.

[0033] <Method of manufacturing conductive ink composition> The first composition is obtained by uniformly mixing the (meth)acrylic polymer (A), silver particles (B), solvent (C), and optional components as required. As the (meth)acrylic polymer (A), a (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and a solvent compatible with (A) may be used. The solvent compatible with the (meth)acrylic polymer (A) may be any of the solvents listed above as examples of the solvent (C), or may be another good solvent (e.g., ethyl acetate). Any known mixing method can be used. For example, the first composition can be produced by premixing all the components in a mixer and kneading the resulting premix several times using a three-roll mill.

[0034] <Conductive film> The first composition is applied to a substrate or the like to form a coating film, and the coating film is dried to remove the solvent (C), thereby obtaining a conductive film. The material and shape of the substrate are not particularly limited. A stretchable substrate is preferable. Examples of stretchable materials include polyurethane, ethylene propylene rubber, silicone rubber, and various elastomers.

[0035] The first composition can be applied to a substrate by a known application method, such as printing, dipping, spraying, or bar coating. From the viewpoints of versatility and accuracy, printing is preferred. Examples of printing methods include inkjet printing, flexographic printing, gravure printing, screen printing, pad printing, lithography printing, etc. In particular, screen printing is preferred because it can easily reduce costs, is suitable for large-area printing, and can easily increase the thickness of the conductive film.

[0036] The coating film may be heated during the drying process. The heating temperature during drying is preferably a temperature that does not adversely affect the substrate and can completely remove the solvent in the coating material. Although this varies depending on the type of substrate, a temperature of 80 to 150°C is preferred, for example. The thickness of the conductive film after drying is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 80 μm. When the thickness is equal to or greater than the lower limit of the above range, conductivity is easily exhibited, and when the thickness is equal to or less than the upper limit, the device to be fabricated can be made smaller.

[0037] The conductive film of the first embodiment is stretchable and conductive, as shown in the examples below. It also has good adhesion to the substrate. Therefore, the first composition can be suitably used as a conductive material for forming wiring, electrodes, etc. on a stretchable substrate, and can achieve good conformity to the stretching of the substrate.

[0038] Furthermore, the conductive film of the first embodiment has excellent resistance to repeated elongation, as will be shown in the examples below, and exhibits good stability of conductivity when elongated repeatedly. According to the first embodiment, for example, it is possible to realize a conductive film whose conductivity is detectable even after repeated elongation at an elongation rate of 100% 100 times. For example, a conductive film can be realized in which the absolute value of the difference in surface resistance (deviation in surface resistance before and after repeated stretching) between before and after (start and end) repeated stretching at an elongation rate of 100% is 100 Ω or less.

[0039] Furthermore, the conductive film of the first embodiment is conductive even in a stretched state, as will be shown in the examples described later. For example, a wearable sensor requires 200% stretchability when applied to the elbow, which is the maximum working area of ​​a human body. According to the first embodiment, a conductive film can be realized that can detect conductivity even when stretched with an elongation rate of 250%, for example.

[0040] Furthermore, the conductive film of the first embodiment can maintain its conductivity in an elongated state even when it is repeatedly elongated, as will be shown in the examples described later. According to the first embodiment, for example, it is possible to realize a conductive film whose conductivity can be detected in a state stretched at an elongation rate of 100%, even when stretched 100 times at an elongation rate of 100%.

[0041] Furthermore, according to the first embodiment, a conductive film whose conductivity (resistance value) changes with a change in shape can be obtained. Specifically, as shown in the examples below, a conductive film can be realized in which the surface resistance increases with increasing elongation. For example, a conductive film can be realized in which the logarithm of the change in resistance (unit: Ω / %) per 1% of elongation when the elongation changes from 0% to 250% is 5.0 or less, preferably 4.0 or less. Such a conductive film, whose resistance value changes with a change in shape, is suitable for use in a resistance change sensor. Specifically, the conductive film of the first embodiment can be used as a resistor (sensing means) in a resistance change sensor. Specific examples of resistance change sensors include wearable or flexible sensors that detect expansion and contraction through changes in electrical resistance, strain sensors that measure strain through changes in electrical resistance, and pressure-sensitive sensors that can sense and measure deformation through changes in electrical resistance. Furthermore, since the conductive film can exhibit high conductivity even when expanded and contracted, it can also be used in conductive components (wiring, electrodes, antennas, heating elements, etc.) that constitute stretchable products. Specific examples include use in conductive components (wiring, electrodes, antennas, etc.) that constitute the wearable sensors, pressure-sensitive sensors, moving parts of robots, artificial muscles, or flexible displays, wiring in in-mold molded parts, and heating elements in flexible heaters. For example, the conductive film of the first embodiment is suitable for use in electrodes that require stretchability in electronic devices, or for use in wiring that requires stretchability in electronic devices. For example, the conductive film of the first embodiment is suitable for use in the detection section of a resistance change type sensor, the electrodes of a resistance change type sensor, or the wiring of a resistance change type sensor.

[0042] Second Embodiment The conductive ink composition of the second embodiment (hereinafter also referred to as "second composition") contains a (meth)acrylic polymer (A) and carbon black (CB) (hereinafter also referred to as (CB) particles). In this specification, the specific surface area of ​​carbon black is a value measured by the BET method, in which nitrogen is adsorbed onto carbon black particles and the specific surface area of ​​the carbon black is measured from the amount of adsorbed nitrogen. The BET specific surface area of ​​carbon black is measured by a method in accordance with ASTM D 3037. In this specification, the aggregate diameter, which is the aggregate of primary particles of carbon black, is a value measured by the method for measuring aggregate diameter described in JIS K6217-6.

[0043] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) in the second embodiment can be the same polymer as the (meth)acrylic polymer (A) in the first embodiment. The (meth)acrylic polymer (A) in the second embodiment can contain the same units (a1) to (a4) as in the first embodiment, and may further contain the unit (a5).

[0044] In the second embodiment, the content of units (a1) relative to all units of the (meth)acrylic polymer (A) is preferably 20 to 40% by mass, more preferably 22 to 38% by mass, and even more preferably 24 to 36% by mass. When the content of units (a1) is at least the lower limit of the above range, a hydroxyl value of more than 50 mgKOH / g is likely to be obtained, and affinity with the (CB) particles is increased, resulting in excellent stretchability. When the content is at most the upper limit, the self-cohesion force of the meth(acrylic) polymer is not too strong, and good dispersibility and good stretchability during ink production are likely to be obtained.

[0045] In the second embodiment, the content of the units (a2) relative to the total units of the (meth)acrylic polymer (A) is preferably 46 to 64 mass%, more preferably 48 to 62 mass%, and even more preferably 50 to 60 mass%. When the content of the units (a2) is equal to or greater than the lower limit of the above range, good durability during stretching is likely to be obtained. When it is equal to or less than the upper limit, the polymer is less likely to become rigid, and good stretchability is likely to be obtained.

[0046] In the second embodiment, the content of the units (a3) ​​relative to all units of the (meth)acrylic polymer (A) is preferably 6 to 19 mass%, more preferably 8 to 17 mass%, and even more preferably 10 to 15 mass%. When the content of the units (a3) ​​is equal to or greater than the lower limit of the above range, excellent flexibility and sufficient stretchability are likely to be obtained. When the content is equal to or less than the upper limit, excellent adhesion to the substrate and good durability during stretching are likely to be obtained.

[0047] In the second embodiment, the content of the units (a4) relative to all units of the (meth)acrylic polymer (A) is preferably 0.05 to 0.35% by mass, more preferably 0.10 to 0.30% by mass, and even more preferably 0.15 to 0.25% by mass. When the content of the units (a4) is equal to or greater than the lower limit of the above range, the affinity with the (CB) particles is excellent and sufficient stretchability is easily obtained. When the content is equal to or less than the upper limit, the cohesive force of the (meth)acrylic acid is not too high and good stretchability is easily obtained.

[0048] In the second embodiment, the content of the units (a5) relative to all units of the (meth)acrylic polymer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. It may be zero.

[0049] The glass transition temperature of the (meth)acrylic polymer (A) in the second embodiment is the same as that in the first embodiment. The weight average molecular weight of the (meth)acrylic polymer (A) in the second embodiment is the same as that in the first embodiment.

[0050] In a second embodiment, the hydroxyl value of the (meth)acrylic polymer (A) is greater than 50 mgKOH / g, preferably 75 mgKOH / g or greater, and more preferably 100 mgKOH / g or greater. When the hydroxyl value exceeds 50 mgKOH / g, the affinity between the (CB) particles and the (meth)acrylic polymer is moderately high, resulting in excellent elasticity. The upper limit of the hydroxyl value is preferably 200 mgKOH / g or less, more preferably 175 mgKOH / g or less, and even more preferably 150 mgKOH / g or less, from the viewpoint of not impairing the conductivity of the (CB) particles.

[0051] In the second embodiment, the (meth)acrylic polymer (A) may be used in the form of a (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and an optional solvent. The solid content of the (meth)acrylic polymer composition is not particularly limited, but from the viewpoint of handling during blending, a viscosity that imparts appropriate fluidity is desirable. For example, a solid content of 10% to 50% by mass is preferred, and 20% to 40% by mass is more preferred.

[0052] A preferred aspect of the (meth)acrylic polymer (A) in the second embodiment is, for example, the above aspect (i).

[0053] <Carbon black (CB)> Carbon black (CB) has a specific surface area of ​​50m 2 / g or more, and the aggregate diameter is 400 nm or less. The specific surface area is 50 to 1300 m 2 / g is preferred, and 55 to 1000m 2 / g is more preferred. The aggregate diameter is preferably 400 nm or less from the viewpoint of not inhibiting stretchability. The lower limit of the aggregate diameter is not particularly limited, but is preferably 100 nm or more, more preferably 150 nm or more, from the viewpoint of exhibiting electrical conductivity. The use of carbon black (CB) that satisfies the above conditions makes it easy to obtain a conductive film that has excellent conductivity when stretched. Furthermore, the combination of the (meth)acrylic polymer (A) and carbon black (CB) that satisfies the above conditions makes it possible to obtain a conductive film that is less likely to crack or break when stretched.

[0054] Examples of carbon black (CB) include those commercially available as conductive carbon black. Specific examples include furnace black, channel black, thermal black, and acetylene black. Furnace black is preferred because it has both elasticity and conductivity. Carbon black (CB) may be used alone or in combination of two or more types.

[0055] <Solvent (C)> The second composition may optionally contain one or more solvents (C). The solvent (C) is not particularly limited as long as it can uniformly disperse the (meth)acrylic polymer (A) and (CB) particles, has low volatility, keeps the ink viscosity stable, and can be removed in the drying step during the formation of the conductive film. The solvent (C) in the second embodiment can be the same compound as the solvent (C) in the first embodiment.

[0056] <Graphite Materials (D)> The second composition may contain one or more graphite materials (D) as a conductive additive. The graphite materials (D) contribute to improving electrical conductivity. Examples of graphite materials include expanded graphite, natural graphite (scale graphite, flake graphite), and artificial graphite. The shape of the graphite material (D) is not particularly limited, but a shape that is flat in one direction, such as a thin flake or a scale, is preferred so as not to inhibit stretchability, and the 50% average particle size is preferably 10 μm to 30 μm. The 50% average particle size of the graphite material (D) is the median diameter at 50% cumulative volume in a particle size distribution curve measured by laser diffraction particle size analysis.

[0057] <Optional ingredients> The second composition may contain optional components other than the (meth)acrylic polymer (A), carbon black (CB), solvent (C), and graphite material (D) to the extent that the effects of the present invention are not impaired. As the optional components, components known in the field of conductive ink compositions can be used. For example, in order to improve printability, components that adjust the interfacial tension of the ink (e.g., surfactants, leveling agents, etc.), components that adjust the viscosity of the ink (e.g., thixotropic agents), etc. may be blended. In addition, in order to improve adhesion to each substrate, it is possible to blend a binder component other than the (meth)acrylic polymer (A). Examples of binder components include polyurethane polymers, epoxy polymers, ester polymers, terpene resins, and terpene resin derivatives (e.g., terpene phenol resins). The binder component can be blended in an amount that does not impair elasticity.

[0058] The solid content of the second composition is 15 to 30% by mass, preferably 16 to 29% by mass, and more preferably 17 to 28% by mass, based on the total mass of the second composition. When the solid content is within the above range, sufficient extensibility and good conductivity when stretched are easily obtained. Furthermore, viscosity suitable for printing is easily obtained. The solid content can be adjusted by the content of the solvent (C).

[0059] The viscosity of the second composition is preferably 20 to 100 Pa·s, more preferably 22 to 98 Pa·s, and even more preferably 24 to 96 Pa·s. When the viscosity is within the above range, good printability is likely to be obtained. For example, properties suitable for screen printing are likely to be obtained. For example, if the viscosity of the second composition is too high, clogging or rubbing may occur during printing, whereas if the viscosity is too low, printing defects such as bleeding and dripping may occur.

[0060] The content of the (meth)acrylic polymer (A) relative to the solid content of the second composition is preferably 40 to 62 mass%, more preferably 41 to 60 mass%, and even more preferably 42 to 58 mass%. When the content of the (meth)acrylic polymer (A) is equal to or greater than the above lower limit, excellent adhesion to the substrate is achieved. Furthermore, sufficient stretchability is easily obtained. When the content is equal to or less than the above upper limit, a sufficient content of the (CB) particles is easily ensured, and good conductivity during stretching is easily obtained. The content of carbon black (CB) relative to the solid content of the second composition is preferably 18 to 50 mass%, more preferably 20 to 48 mass%, and even more preferably 22 to 46 mass%. When the content of carbon black (CB) is equal to or greater than the above-mentioned lower limit, good conductivity is likely to be obtained. When the content is equal to or less than the above-mentioned upper limit, it is easy to ensure a sufficient content of components other than (CB) particles, and good properties such as stretchability are likely to be obtained. In addition, the viscosity does not become too high, and printing defects such as rubbing are unlikely to occur. The content of the optional components relative to the solid content of the second composition is preferably 30% by mass or less, more preferably 25% by mass or less, and may be zero.

[0061] When the second composition contains the graphite material (D), the content of the graphite material (D) is preferably 16 to 30 mass %, more preferably 18 to 28 mass %, and even more preferably 20 to 26 mass %, relative to the solid content of the second composition. When the content of the graphite material (D) is equal to or greater than the above lower limit, the effect of improving conductivity is excellent, and when it is equal to or less than the above upper limit, the conductive film is less likely to become hard and good stretchability is likely to be obtained. Furthermore, when the second composition contains a graphite material (D), the proportion of carbon black (CB) relative to the total mass of carbon black (CB) and the graphite material (D) is preferably 40 to 80 mass%, more preferably 45 to 70 mass%, and even more preferably 50 to 60 mass%. When the proportion of carbon black (CB) is equal to or greater than the lower limit, the conductive film is less likely to become hard and good stretchability is likely to be obtained. When the proportion is equal to or less than the upper limit, the graphite material (D) is likely to have an effect of improving conductivity. When the second composition contains other conductive carbon materials, the proportion of the other conductive carbon materials is preferably 5 mass% or less, more preferably 3 mass% or less, relative to the total mass of the carbon black (CB), the graphite material (D), and the other conductive carbon materials.

[0062] <Method of manufacturing conductive ink composition> The second composition is obtained by uniformly mixing the (meth)acrylic polymer (A), carbon black (CB), solvent (C), and optionally the graphite material (D) and optional components. As the (meth)acrylic polymer (A), a (meth)acrylic polymer composition containing the (meth)acrylic polymer (A) and a solvent compatible with (A) may be used. The solvent compatible with the (meth)acrylic polymer (A) may be any of the solvents listed above as examples of the solvent (C), or may be another good solvent (e.g., ethyl acetate). The mixing method can be the same as that in the first embodiment.

[0063] <Conductive film> The second composition is applied to a substrate or the like to form a coating film, and the coating film is dried to remove the solvent (C), thereby obtaining a conductive film. The material and shape of the substrate can be the same as those in the first embodiment.

[0064] The second composition can be applied to the substrate by the same method as in the first embodiment.

[0065] As in the first embodiment, the coating film may be heated in the drying step. The thickness of the conductive film after drying can be the same as in the first embodiment.

[0066] The conductive film of the second embodiment is stretchable and conductive, as shown in the examples below. It also has good adhesion to the substrate. Therefore, the second composition can be suitably used as a conductive material for forming wiring, electrodes, etc. on a stretchable substrate, and can achieve good conformity to the stretching of the substrate. For example, if the detection limit for surface resistance is 1.0 x 10 7 (Ω) or less, a conductive film can be realized with an elongation at which the surface resistance can be measured of 300% or more, preferably 350% or more.

[0067] Furthermore, the conductive film of the second embodiment has excellent resistance to repeated elongation, as will be shown in the examples below, and exhibits good stability of conductivity when elongated repeatedly. According to the second embodiment, for example, it is possible to realize a conductive film whose conductivity is detectable even after repeated elongation at an elongation rate of 100% 100 times. For example, if the stretching is repeated 100 times at 100% elongation, the absolute value of the difference in surface resistance (deviation in surface resistance before and after repeated stretching) is 5.0 x 10 4 A conductive film with a resistance of Ω or less can be realized.

[0068] Furthermore, the conductive film of the second embodiment is conductive even in a stretched state, as will be shown in the examples described later. For example, a wearable sensor requires 200% stretchability when applied to the elbow, which is the maximum working area of ​​a human body. According to the second embodiment, a conductive film can be realized that can detect conductivity even when stretched with an elongation rate of 300%, for example.

[0069] Furthermore, the conductive film of the second embodiment can maintain its conductivity in an elongated state even when it is repeatedly elongated, as will be shown in the examples described later. According to the second embodiment, for example, it is possible to realize a conductive film whose conductivity can be detected in a state stretched at an elongation rate of 100%, even when stretched 100 times at an elongation rate of 100%.

[0070] Furthermore, according to the second embodiment, a conductive film whose conductivity (resistance value) changes with a change in shape can be obtained. Specifically, as shown in the examples below, a conductive film can be realized in which the surface resistance increases with increasing elongation. For example, a conductive film can be realized in which the logarithm of the change in resistance (unit: Ω / %) per 1% of elongation when the elongation changes from 0% to 300% is 5.0 or less, preferably 4.5 or less. Such a conductive film whose resistance value changes with a change in shape is suitable for use in a resistance change sensor. Specifically, the conductive film of the second embodiment can be used as a resistor (sensing means) in a resistance change sensor. Specific examples of resistance change sensors include wearable or flexible sensors that detect expansion and contraction through changes in electrical resistance, strain sensors that measure strain through changes in electrical resistance, and pressure-sensitive sensors that can sense and measure deformation through changes in electrical resistance. Furthermore, since the conductive film can exhibit high conductivity even when expanded and contracted, although not as highly conductive as metal inks using metal fillers, it can also be used in conductive members (wiring, electrodes, heaters, etc.) that constitute stretchable articles. Specific examples include use in conductive members (wiring, electrodes, etc.) that constitute the wearable sensors, pressure-sensitive sensors, and biosensors (e.g., glucose sensors), as well as in heating elements of flexible heaters. For example, the conductive film of the second embodiment is suitable for use in electrodes that require stretchability in electronic devices, or for use in wiring that requires stretchability in electronic devices. For example, the conductive film of the second embodiment is suitable for use in the detection section of a resistance change type sensor, the electrodes of a resistance change type sensor, or the wiring of a resistance change type sensor. [Example]

[0071] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description. In the following, the unit of content "%" is "% by mass" unless otherwise specified.

[0072] <Production Example of (Meth)acrylic Polymer Composition> The monomers shown in Tables 1 and 7 are as follows: [Hydroxyl group-containing monomer (a1)] 2HPA: 2-hydroxypropyl acrylate 4HBA: 4-hydroxybutyl acrylate 2HEA: 2-hydroxyethyl acrylate 2HEMA: 2-hydroxyethyl methacrylate [C4-12 alkyl (meth)acrylate (a2)] BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate [C1-3 alkyl (meth)acrylate (a3)] MA: methyl acrylate MMA methyl methacrylate [Carboxy group-containing monomer (a4)] AA: acrylic acid [Other monomers (a5)] Vac: Vinyl acetate

[0073] (Production Example 1-1: Production of (meth)acrylic polymer composition (1-1)) The monomer mixture shown in Table 1 was polymerized in a polymerization solvent to synthesize a (meth)acrylic polymer, and further solvent was added to adjust the solid content concentration to obtain a (meth)acrylic polymer composition. Specifically, 29.8 parts by mass of 2HPA, 57.2 parts by mass of BA, 12.8 parts by mass of MA, and 0.2 parts by mass of AA as monomers, 0.02 parts by mass of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 43 parts by mass of ethyl acetate as a polymerization solvent were placed in a separable flask. Nitrogen gas was introduced to remove oxygen from the polymerization system, and the temperature was raised to 70 ° C. and the reaction was carried out for 8 hours to obtain (meth)acrylic polymer A1-1. Ethyl acetate was added to this to adjust the solids concentration to 33% by mass, and a (meth)acrylic polymer composition (1-1) was obtained. The glass transition temperature, weight average molecular weight and hydroxyl value of the (meth)acrylic polymer are shown in Table 1 (the same applies hereinafter).

[0074] (Production Examples 1-2 to 1-5: Production of (meth)acrylic polymer compositions (1-2) to (1-5)) The composition of the monomer mixture was changed as shown in Table 1, and the monomer mixture was polymerized in the same manner as in Production Example 1 to synthesize (meth)acrylic polymers A1-2 to A1-5. Ethyl acetate was added to this to adjust the solid content concentration as shown in Table 1, thereby obtaining (meth)acrylic polymer compositions (1-2) to (1-5).

[0075] (Comparative Composition (1-6)) As a comparative composition (1-6), a polyester resin solution (product name "Nichigo Polyester LP-035" manufactured by Mitsubishi Chemical Corporation) was used. Table 1 shows the glass transition temperature, weight average molecular weight, and hydroxyl value of the polyester resin in the comparative composition (1-6) (comparative resin P1-6).

[0076] [Table 1]

[0077] <Silver particles (B)> The following silver particles were used. Table 2 shows the shape, specific surface area, 50% average particle size, and maximum particle size of each silver particle. Silver particles (B1): Tokuriki Kogyo Co., Ltd. product name "Sylbestos TC-12", thin flake particles. Silver particles (B2): Fukuda Metal Foil & Powder Industries Co., Ltd. product name "AgC-2011", flaky particles. Silver particles (B3): Tokuriki Kogyo Co., Ltd. product name "Sylbestos TC-725", thin flake particles. Silver particles (B4): Mitsui Mining & Smelting Co., Ltd. product name "SLO2", spherical particles. Silver particles (B5): Tokusen Kogyo Co., Ltd. product name "M612", thin flake particles.

[0078] <Solvent (C)> The following solvents were used: Solvent (C1-1): Diethylene glycol monoethyl ether acetate Solvent (C1-2): Polyoxypropylene 2-ethylhexyl ether derivative (Aoki Oil & Fat Co., Ltd. product name "Brownon EHP-4")

[0079] <Optional ingredients> The following optional ingredients were used: Optional ingredient (1-1): Binder, terpene phenol resin (Yasuhara Chemical Co., Ltd. product name "YS Polyster T80") Optional ingredient (1-2): Ion scavenger (Toagosei Co., Ltd. product name "IXEPLAS-A2")

[0080] [Table 2]

[0081] (Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-8) Silver particles and a solvent were blended into the (meth)acrylic polymer composition according to the formulations shown in Tables 3 to 6. In Example 1-5, optional component (1-1), silver particles, and a solvent were blended into the (meth)acrylic polymer composition. In Comparative Example 1-4, silver particles and a solvent were blended into the comparative composition (1-6). All the ingredients were premixed using a mixer and then kneaded using a three-roll mill (Imex product name "BR-150VIII") to obtain a conductive ink composition. The kneading was carried out twice at a rotation speed of 120 rpm and a roll distance of 40 μm, and then the roll distance was reduced to 10 μm and the kneading was carried out two more times. The table shows the solid content, (meth)acrylic polymer (A) content, and silver particle (B) content relative to the total mass of the conductive ink composition for each example. The table also shows the (meth)acrylic polymer (A) content and silver particle (B) content relative to the solid content. The table also shows the viscosity of the conductive ink composition. A blank space in the table means that the component is not included.

[0082] Evaluation Method The resulting conductive film was evaluated by the following methods. The conductive ink composition obtained in each example was applied to a substrate and dried at 130°C for 10 minutes to produce a laminate having a conductive film on the substrate. The substrate was a stretchable polyurethane sheet (thickness: 100 μm). The dry thickness of the conductive film was approximately 30 μm. The conductive films obtained were evaluated for the following items, and the results are shown in Tables 3 to 6.

[0083] (Volume resistivity measurement) The laminate obtained in each example was used as a sample, and the volume resistance value (unit: Ω·cm) of the conductive film was measured using the four-terminal electrodes of a resistivity meter (product name "Loresta" by Nitto Seiko Analytech Co., Ltd.). The thickness of the conductive film was measured using a microgauge.

[0084] (Evaluation of Adhesion) The laminate obtained in each example was used as a sample and a peel test was performed using the cross-cut method based on JIS: K5600-5-6. Specifically, the conductive film of the laminate was cross-cut with a cutter knife so that 100 squares with 1 mm sides were formed on the conductive film. Cellotape (registered trademark) was attached to this conductive film and peeled off in the vertical direction, and the degree of peeling of the conductive film was evaluated according to the following criteria. The case where none of the 100 squares peeled off was marked "◯", the case where squares 1 to 99 peeled off was marked "△", and the case where all of the 100 squares peeled off was marked "X".

[0085] (Extension test) The laminate obtained in each example was cut into a No. 3 dumbbell shape and used as a sample, which was then set in a tensile tester. The distance between the gauge lines (initial dimension) was 20 mm, and the specimen was pulled at a tensile speed of 10 mm / min at 23°C, and the surface resistance (unit: Ω) between the gauge lines was measured at each specific elongation using a tester (Custom Co., Ltd., product name "CDM-2000D"). The elongation percentage is a value calculated by the following formula. Elongation rate (%) = (distance between gauge lines after elongation (mm) - initial dimension) / initial dimension × 100 When the elongation rate is 200% (200% elongation), that is, when the distance between the gauge lines is 60 mm, the surface resistance R 1 is shown in the table. In addition, when the elongation rate is 250% (250% elongation), that is, when the distance between the gauge lines is 70 mm, the surface resistance R 2 is shown in the table. The table also shows the logarithmic value of the resistance change (unit: Ω / %) per 1% elongation when the elongation rate changes from 0% to 250%, calculated using the following formula (3). R in formula (3) 0 indicates the surface resistance value when the elongation rate is 0% (0% elongation). If the film cracked or broke during elongation, it was marked as "× (not achieved)", and if it was elongated but conductivity could not be detected, it was marked as "× (impossible to measure)".

[0086]

number

[0087] (Repeated extension test) The laminate obtained in each example was cut into a No. 3 dumbbell shape and used as a sample, which was then set in a tensile tester. The distance between the gauge lines (initial dimension) was set to 20 mm, and repeated elongation was performed at 23°C and a tensile speed of 500 mm / min. Specifically, the first cycle was stretching from the initial dimensions (0%, gauge length 20 mm) to an elongation rate of 100% (gauge length 40 mm) and then returning to an elongation rate of 0% (gauge length 20 mm), and the second cycle was stretching from an elongation rate of 0% to an elongation rate of 100%, and then returning to an elongation rate of 0%. This cycle was repeated up to 100 times. Every 10 cycles, the surface resistance value (unit: Ω) between the gauge lines was measured using the resistivity meter. The table shows the surface resistance at the start (0%), the surface resistance when stretched to 100% on the first stretch, the surface resistance when stretched to 100% on the 100th stretch, and the surface resistance when the stretch rate was returned to 0% after the 100th stretch (end 0%). The deviation in surface resistance before and after the repeated elongation test was also evaluated. The difference in surface resistance between 0% at the end and 0% at the start is shown in absolute value in the table. If the film cracked or broke during the first or 100th stretch, it was marked as "x (not achieved)."

[0088] [Table 3]

[0089] [Table 4]

[0090] [Table 5]

[0091] [Table 6]

[0092] As shown in Tables 3 and 4, the conductive films of Examples 1-1 to 1-8 were excellent in conductivity and adhesion to the substrate, and were also stretchable and had excellent conductivity when stretched, with conductivity being detectable even when stretched by 250%. The conductive films of Examples 1-1 to 1-8 also had excellent resistance to repeated elongation, and even after repeated elongation at 100% elongation 100 times, conductivity was detectable both in the elongated state (100)% and in the non-elongated state (0%). Furthermore, the stability of conductivity when repeatedly elongated was excellent, and the deviation in surface resistance value before and after the repeated elongation test was small. Furthermore, in Examples 1-1 to 1-8, a tendency was observed in which the surface resistance value increased as the elongation increased.

[0093] On the other hand, as shown in Tables 5 and 6, in Comparative Examples 1-1 to 1-3 in which the glass transition temperature, weight average molecular weight, or hydroxyl value of the (meth)acrylic polymer (A) was outside the range of the present invention, and in Comparative Example 1-4 in which a comparative resin (polyester) was used instead of the (meth)acrylic polymer (A), cracks or breaks occurred in the film during elongation in the elongation test and repeated elongation test. In Comparative Example 1-5, in which the maximum particle size of the silver particles was too small, cracks or breaks occurred in the film during the elongation test, and the surface resistance value could not be detected at elongation of 200% or more. In Comparative Example 1-6, in which the 50% average particle size and maximum particle size of the silver particles were too small, cracks or breakage occurred in the film in the elongation test and repeated elongation test. In Comparative Example 1-7, in which the solid content of the conductive ink composition was too low, the conductive film could be stretched up to 250% in the elongation test, but the surface resistance value could not be detected.In the repeated elongation test, the conductive film could withstand repeated elongation of 100% x 100 times, but the surface resistance value could not be detected. In Comparative Example 1-8, in which the solid content of the conductive ink composition was too high, cracks or breaks occurred in the film in the extension test and repeated extension test.

[0094] (Production Example 2-1: Production of (meth)acrylic polymer composition (2-1)) The monomer mixture shown in Table 7 was polymerized in a polymerization solvent to synthesize a (meth)acrylic polymer, and further solvent was added to adjust the solid content concentration to obtain a (meth)acrylic polymer composition. Specifically, 29.8 parts by mass of 2HPA, 57.2 parts by mass of BA, 12.8 parts by mass of MA, and 0.2 parts by mass of AA as monomers, 0.02 parts by mass of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 43 parts by mass of ethyl acetate as a polymerization solvent were placed in a separable flask. Nitrogen gas was introduced to remove oxygen from the polymerization system, and the temperature was raised to 70 ° C. and the reaction was carried out for 8 hours to obtain (meth)acrylic polymer A2-1. Ethyl acetate was added to this to adjust the solids concentration to 33% by mass, and a (meth)acrylic polymer composition (2-1) was obtained. The glass transition temperature, weight average molecular weight and hydroxyl value of the (meth)acrylic polymer are shown in Table 7 (the same applies hereinafter).

[0095] (Production Examples 2-2 and 2-3: Production of (meth)acrylic polymer compositions (2-2) and (2-3)) The composition of the monomer mixture was changed as shown in Table 7, and the monomer mixture was polymerized in the same manner as in Production Example 2-1 to synthesize (meth)acrylic polymers A2-2 and A2-3. Ethyl acetate was added to this to adjust the solid content concentration as shown in Table 7, thereby obtaining (meth)acrylic polymer compositions (2-2) and (2-3).

[0096] (Comparative Composition (2-4)) As a comparative composition (2-4), a polyester resin solution (product name "Nichigo Polyester LP-035" manufactured by Mitsubishi Chemical Corporation) was used. Table 7 shows the glass transition temperature, weight average molecular weight, and hydroxyl value of the polyester resin in the comparative composition (2-4) (comparative resin P2-4).

[0097] [Table 7]

[0098] <Carbon black (CB)> The following (CB) particles were used. The specific surface area and aggregate diameter of each (CB) particle are shown in Table 8. Carbon black (CB1): Lion Specialty Chemicals product name "Ketjenblack EC300J", furnace black. Carbon black (CB2): Imerys product name "Ensaco250G", furnace black. Carbon black (CB3): Denka product name "Denka Black HS-100", acetylene black.

[0099] The following raw materials were used: <Solvent (C)> Solvent (C2-1): Diethylene glycol monoethyl ether acetate. <Graphite Materials (D)> Graphite (D2-1): Shin-Etsu Chemical Co., Ltd. product name "BSP-20A", expanded graphite, flake-like, average particle size 20 μm. <Dispersant (E)> Dispersant (E2-1): Kusumoto Chemicals Co., Ltd. product name "DA-1200", high molecular weight unsaturated polycarboxylic acid.

[0100] [Table 8]

[0101] (Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-7) Carbon black, a graphite material, a dispersant, and a solvent were blended into the (meth)acrylic polymer composition according to the formulations shown in Tables 9 to 11. In Comparative Examples 2-3 and 2-4, carbon black, a graphite material, a dispersant, and a solvent were blended into the comparative composition (2-4). All the ingredients were premixed using a mixer and then kneaded using a three-roll mill (Imex product name "BR-150VIII") to obtain a conductive ink composition. The kneading was carried out twice at a rotation speed of 120 rpm and a roll distance of 40 μm, and then the roll distance was reduced to 10 μm and the kneading was carried out two more times. The table shows the solid content, (meth)acrylic polymer (A) content, and carbon black (CB) content relative to the total mass of the conductive ink composition for each example. The table also shows the (meth)acrylic polymer (A) content, carbon black (CB) content, and graphite material (D) content relative to the solid content. The table also shows the viscosity of the conductive ink composition. A blank space in the table means that the component is not included.

[0102] Evaluation Method The resulting conductive film was evaluated by the following methods. The conductive ink composition obtained in each example was applied to a substrate and dried at 130°C for 10 minutes to produce a laminate having a conductive film on the substrate. The substrate was a stretchable polyurethane sheet (thickness: 100 μm). The dry thickness of the conductive film was approximately 30 μm. The obtained conductive films were evaluated for the following items, and the results are shown in Tables 9 to 11.

[0103] (Volume resistivity measurement) The volume resistivity was measured in the same manner as in Example 1-1. (Evaluation of Adhesion) The adhesion was evaluated in the same manner as in Example 1-1.

[0104] (Extension test (1)) The laminate obtained in each example was cut into a No. 3 dumbbell shape and used as a sample, which was then set in a tensile tester. The distance between the gauge lines (initial dimension) was 20 mm, and the specimen was pulled at a tensile speed of 10 mm / min at 23°C, and the surface resistance (unit: Ω) between the gauge lines was measured at each specific elongation using a tester (Custom Co., Ltd., product name "CDM-2000D"). The elongation percentage is a value calculated by the following formula. Elongation rate (%) = (distance between gauge lines after elongation (mm) - initial dimension) / initial dimension × 100 When the elongation rate is 200% (200% elongation), that is, when the distance between the gauge lines is 60 mm, the surface resistance R 1 is shown in the table. In addition, when the elongation rate is 300% (300% elongation), that is, when the distance between the gauge lines is 80 mm, the surface resistance R 2 is shown in the table. The table also shows the logarithmic value of the resistance change (unit: Ω / %) per 1% elongation when the elongation rate changes from 0% to 300%, calculated using the following formula (4). R in formula (4) 0 indicates the surface resistance value when the elongation rate is 0% (0% elongation). If the film cracked or broke during elongation, it was marked as "× (not achieved)", and if it was elongated but conductivity could not be detected, it was marked as "× (impossible to measure)".

[0105]

number

[0106] (Extension test (2)) Using the same measurement method as in the elongation test (1), the surface resistance (unit: Ω) was measured by gradually increasing the elongation rate. The elongation rate was increased by 25% from 50% to 100%, and then increased by 50% after exceeding 100%. 7 The maximum elongation at which the surface resistance could be measured was 1.0 x 10 7 The maximum elongation (unit: %) below Ω was recorded.

[0107] (Repeated extension test) Repeated extension tests were carried out in the same manner as in Example 1-1, and the items shown in the table were evaluated.

[0108] [Table 9]

[0109] [Table 10]

[0110] [Table 11]

[0111] As shown in Table 9, the conductive films of Examples 2-1 to 2-5 were excellent in conductivity and adhesion to the substrate. They were also stretchable and had excellent conductivity when stretched. Even at 300% stretch, the conductivity was detectable, reaching 1.0 × 10 7 The maximum elongation rate was large below Ω. The conductive films of Examples 2-1 to 2-5 also had excellent resistance to repeated elongation, and even after repeated elongation at 100% elongation 100 times, conductivity was detectable in both the elongated state (100)% and the non-elongated state (0%). Furthermore, the stability of conductivity when repeatedly elongated was excellent, and the deviation in surface resistance value before and after the repeated elongation test was small. Furthermore, in Examples 2-1 to 2-5, a tendency was observed in which the surface resistance value increased as the elongation increased.

[0112] On the other hand, as shown in Tables 10 and 11, in Comparative Examples 2-1 and 2-2 in which the weight average molecular weight or hydroxyl value of the (meth)acrylic polymer (A) was outside the range of the present invention, and in Comparative Examples 2-3 and 2-4 in which a comparative resin (polyester) was used instead of the (meth)acrylic polymer (A), cracks or breaks occurred in the membrane during elongation in the elongation test and repeated elongation test. In Comparative Example 2-5, in which the solid content of the conductive ink composition was too low, and Comparative Example 2-6, in which the solid content was too high, cracks or breaks occurred in the film in the extension test and repeated extension test. In Comparative Example 2-7, in which the specific surface area of ​​the carbon black (CB) was small and the aggregate diameter was large, cracks or breaks occurred in the film in the extension test and repeated extension test.

Claims

1. A composition comprising a (meth)acrylic polymer (A) and silver particles (B), the (meth)acrylic polymer (A) has a glass transition temperature of more than −50° C. and not more than 0° C., a weight average molecular weight of 500,000 to 990,000, and a hydroxyl value of more than 50 mgKOH / g and not more than 200 mgKOH / g, The silver particles (B) have a specific surface area of ​​0.5 to 3.0 m ２ / g, 50% average particle size is 0.5 to 14.0 μm, and maximum particle size is 8 μm or more, A conductive ink composition having a solid content of 50 to 80 mass %.

2. 2. The conductive ink composition according to claim 1, wherein the (meth)acrylic polymer (A) has a glass transition temperature of more than -50°C and less than -30°C.

3. 2. The conductive ink composition according to claim 1, wherein the content of units (a1) derived from a hydroxyl group-containing monomer is 20 to 40 mass % relative to all units constituting the (meth)acrylic polymer (A).

4. 2. The conductive ink composition according to claim 1, wherein the viscosity at 23° C. is 20 to 50 Pa·s.

5. A conductive film obtained by drying a coating of the conductive ink composition according to any one of claims 1 to 4.

6. The conductive film according to claim 5 , which is used for electrodes or wiring that require stretchability in electronic devices.

7. The conductive film according to claim 5 , which is used for a detection part, an electrode, or a wiring of a resistance change type sensor.

8. Contains a (meth)acrylic polymer (A) and carbon black (CB), the (meth)acrylic polymer (A) has a glass transition temperature of more than −50° C. and not more than 0° C., a weight average molecular weight of 500,000 to 990,000, and a hydroxyl value of more than 50 mgKOH / g and not more than 200 mgKOH / g, The specific surface area of ​​the carbon black (CB) is 50 m ２ / g or more, and the aggregate diameter is 400 nm or less, A conductive ink composition having a solid content of 15 to 30 mass %.

9. The conductive ink composition according to claim 8, wherein the (meth)acrylic polymer (A) has a glass transition temperature of more than -50°C and less than -30°C.

10. 9. The conductive ink composition according to claim 8, wherein the content of units (a1) derived from a hydroxyl group-containing monomer is 20 to 40 mass % relative to all units constituting the (meth)acrylic polymer (A).

11. 9. The conductive ink composition according to claim 8, which has a viscosity at 23° C. of 20 to 100 Pa·s.

12. A conductive film obtained by drying a coating of the conductive ink composition according to any one of claims 8 to 11.

13. The conductive film according to claim 12, which is used for electrodes or wiring that require stretchability in electronic devices.

14. The conductive film according to claim 12, which is used for a detection section, an electrode, or a wiring of a resistance change type sensor.

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